1. Field
Embodiments of the disclosure relate generally to aerodynamic flow control and more particularly to embodiments for a synthetic jet actuation system for increasing the air flow velocity and air flow volume through resonant vibration of a fluid in a sealed cavity with a flexible diaphragm induced by a piezo actuator.
2. Background
Synthetic Jet Actuators (Net Zero Mass Actuators) are placed in an aerodynamic lifting surface to improve the aerodynamic efficiency of the lifting surface. A common method of generating a synthetic jet employs a cavity with an orifice formed by a hole or slot and an actuator closing the cavity opposite the aperture. An example synthetic jet generator consists of a sealed cavity with an orifice and an opposing flexible vibrating diaphragm. Actuator operation employs a cycle with two strokes; a suction and an ejection. During the suction stroke the diaphragm moves away from the orifice, increasing the volume of the cavity and subsequently decreasing the pressure within. During the ejection stroke, the diaphragm moves toward the orifice, resulting in the expulsion through the orifice of fluid accumulated in the cavity during the suction stroke.
Two nondimensional variables the stroke ratio (L/d) and Reynolds number, Re, are the primary factors that influence synthetic jet performance. The ejected fluid is defined as L/d≈ΔD2/d3 where L is the length of a column of ejected fluid and d is the orifice diameter, D is the diaphragm diameter and Δ is the diaphragm displacement.
Thus increasing the diaphragm displacement, Δ, will increase the stroke length and the corresponding exit velocity and momentum of the synthetic jet.
Current synthetic jet actuators employ Piezo electric actuators as the diaphragm. Presently Piezo electric actuators are manufactured with ceramics. They are noted for generation of large forces and small deflections. As alternating electrical voltage is applied, the Piezo will bend in different directions. Attempts at a solution for additional stroke length involve development of more flexible Piezo electric actuators that vibrate inside the cavity of the synthetic jet actuator to increase the exit jet stream velocity. Present technology is manufacturing Piezo electric bender actuators to be more flexible but their deflection or strains remain relatively small. This limits the diaphragm deflected motion of the synthetic jet actuator and limits the available performance.
It is therefore desirable to provide a system which enhances the deflected motion of the diaphragm in a synthetic jet actuator for increased performance.